Diesel Engines & Their Efficiency

It’s been widely acknowledged that diesel engines provide better fuel mileage than gas engines because they’re fundamentally more efficient.  But, how true is this? Thank you to the Service team at Fletcher Chrysler Products, a Chrysler, Dodge, Jeep and RAM full-service car dealership in Franklin, IN for their insight!

Where can you find diesel engines? They are often found on large transport vehicles, like trucks and busses. However, they are also found on airplanes, boats and even motorcycles. Sometimes they are even found on construction equipment and agricultural tractors. So next time you get behind a farm tractor on the road you might get thinking about diesel engines.

A Bit About Diesel Engine History

The Diesel engine is named after Rudolf Diesel, who was born in Paris in 1858. He invented the Diesel engine while the steam engine was the main engine used. He got going on his engine in 1885 in Paris, and he was hoping to develop a compression ignition engine, and the process for that lasted thirteen years. Diesel was reported missing in 1913, but other companies took on his invention and further developed it.

Diesel Engine Efficiency

Let’s examine the efficiency argument. A diesel engine’s higher compression ratio and lean-burn combustion cycle provide an efficiency that a gas engine can’t presently attain. Over the diesel’s operating range, the average “thermodynamic efficiency”—how much energy an engine receives from the fuel—is at least 15% better than a gas engine.  Big advantage diesel? 

The reality is that this lead is shrinking quick. As emissions regulations get stronger, diesels are losing their lead in the efficiency race.  A big issue is that many of today’s diesel engines need scrubbers to clean up the dirty diesel exhaust. And these units happen to crimp the efficiency of the system due to their design. They soak up some of the additional energy that the diesel fuel provides. 

The Future of Diesel Engines

Gas engines keep improving. Once-exotic efficiency-enhancing hardware like direct fuel injection, turbochargers and variable camshaft timing have become commonplace on gasoline engines.  And there is more on the way, like homogeneous charge compression ignition and lean-burn combustion. However, while their gasoline powered relatives continue to get better, don’t expect the diesel engine to remain static.  Around the world, engineers are working hard to improve the efficiency of diesel engines more. These gains will come from hardware like independent cylinder combustion control and variable valve timing, as well as fantastic after-treatment systems for diesel exhaust.   

Final Remarks

As you can see, this race is far from called.  What’s interesting is that while Diesel engines are becoming better accepted here in the US, they make up over 50% of sales in Europe. The reason for that is probably due to an open mind about diesel engines rather than than pure economics, though. US manufacturers have made some poor diesel engines in the past, such as the interesting 350 Oldsmobile Diesel in the 1970s, and that has slowed American acceptance. Hopefully you have enjoyed this look into diesel engines!